Comparative local anaesthetic blocks in the diagnosis of cervical zygapophysial joint pain.

The utility of randomised, double-blind, controlled, comparative local anaesthetic blocks for the diagnosis of cervical, zygapophysial joint pain was studied in 47 patients with chronic neck pain following whiplash injury. Each patient was investigated with radiologically controlled blocks of the medial branches of the cervical, dorsal rami to anaesthetise the target cervical, zygapophysial joint. The blocks were performed using either lignocaine or bupivacaine, randomly allocated, and the patients' responses were assessed in a double-blind fashion. Any positive response was subsequently assessed by repeating the block with the complementary anaesthetic. Only those patients experiencing a longer period of pain relief from the bupivacaine were considered to have true-positive responses. Forty-four patients had pain relief from two blocks at a single level, of whom 34 had longer pain relief from bupivacaine. This result is unlikely to have occurred by chance (P = 0.0002). The durations of pain relief obtained from the anaesthetics were consistent with the known characteristics of these drugs with bupivacaine lasting significantly longer than lignocaine (P = 0.0003). A subgroup of 13 patients were identified with unexpected, prolonged responses to one or both of the anaesthetics. Comparative, diagnostic blocks are a valid technique in the identification of painful zygapophysial joints, and constitute an implementable alternative to normal saline controls.